Pin-barrel extruders are known and comprise a screw conveyor which is rotatable in the hollow interior of a barrel. Disposed along the length of the barrel and projecting radially into the hollow interior of the barrel are a plurality of pins. These pins project to adjacent the core of the screw, the flight or flights on the screw being discontinuous in the region of the pins.
It is desirable if the depth of penetration of the pins into the barrel is adjustable. Such an arrangement is disclosed in U.S. Pat. No. 4,178,104. In such arrangement the pins are screw-fitted in holding members and are non-rotatably connected thereto by means of lock nuts. The holding fixtures are radially displaceable in guide members mounted on the extruder cylinder. A gear member is used for adjustment purposes. One face of the gear faces the holding fixture and is provided with a cam track. The track engages corresponding complementary cam-followers on the holding fixtures. The gear member is driven by a pinion, is freely rotatable and is prevented from axial movement by a collar ring.
However, such an arrangement suffers from numerous disadvantages. In setting up such an arrangement, the gear member must firstly be positioned over the extruder barrel. In its end position, it then has to be mounted on a sleeve-like guide means which, in turn, has to be screw-connected to the extruder barrel. Finally, complementary cams and cam tracks have to be provided laterally on the gear member and in the holding fixtures. This is time-consuming and costly.
In addition, an extremely elaborate construction is also required, for the mounting of the drive pinion which engages with the gear on the extruder cylinder. This adds to the costs associated with the production of an extruder having such an adjustment arrangement.
It is also difficult to assemble the adjusting means. Before a barrel flange connecting member, which is usually provided to permit barrel portions to be connected together, is welded to one end of a barrel portion, it is necessary for the sleeve-like guide member to be slid onto the barrel so as to receive the bearings for the gear. The gear is then positioned over the cylinder and brought into its intended position. Only after this has been done can the guide member be screw-connected to the extruder barrel. The holding fixture, which is provided with the lateral cam followers, is then slid onto the extruder barrel into its intended position. The individual pins are screwed radially inwardly through the holding fixture. Only when the assembly of all of these integers has been completed, can the barrel flange be welded to the end of the barrel portion.
After a period of time, it is likely that the cam followers on the holding fixture and the cam track on the gear member will exhibit signs of wear. To replace them, the above-described procedure must be reversed. So much work is involved that it is simpler to replace the entire barrel portion. Moreover, it is also necessary to extract the screw from the extruder, and to remove the barrel flange connection. These measures which need to be taken mean that the extruder is inoperative for long, and therefore costly, periods of time.